This invention relates to an actuator of an air-bag type extensible and contractible in axial directions by supplying and exhausting a pressurized fluid.
There has been known an actuator, for example, as shown in FIG. 1 as an air-bag type actuator capable of converting energy of a pressurized fluid into kinetic energy with high efficiency.
This actuator 10 includes a tubular body 12, a reinforcing braided structure 14 externally arranged thereon, and closure members 16 closing both ends of the tubular body 12 and the reinforcing braided structure 14. When a pressurized fluid is supplied into an internal space 20 of the tubular body 12 through a connecting aperture 18 formed in at least one of the closure members 16, an enlargement of initial braided angles .theta. of the reinforcing braided structure 14 or a pantograph movement of the braided structure 14 causes an expansion of a diameter of the tubular body 12 and a contraction of the body 12 in axial directions owing thereto or a contraction of a distance between both the closure members 16. Such an actuator has various advantages in that it is very light weight because of the construction above described and compliance as an actuator can be suitably changed by adjusting pressure of the pressurized fluid to be supplied.
In general, the tubular body 12 is preferably made of a rubber or rubber-like elastic material or a material equivalent thereto in consideration of impermeability to pressurized fluids and sufficient flexibility. The reinforcing braided structure 14 is preferably made of organic or inorganic high tension fibers having braided structures whose braided angles vary from initial braided angles, for example, 10.degree. to 25.degree. to so-called "angle of repose" (54.degree.44') when the tubular body expands at a maximum diameter.
With such an actuator, when the pressurized fluid is exhausted from the internal space 20, the actuator can return to its original shape with the aid of an elastic returning force of the tubular body 12. However, as the returning force is not sufficient, it is necessary to provide an elastic member such as a compression spring assisting in returning of the actuator to its original shape.
However, as the elastic member such as a compression spring has an invariable spring constant and a constant outer diameter, it will encounter a difficulty when it is required to change the compliance of the actuator including the elastic member and its outer shape and size. In this case, it is again needed to design and manufacture a spring member whose spring constant and outer diameter and outer size need respective requirements.